Ethylene resin foamed products

ABSTRACT

The present invention provides an ethylene resin foamed product containing uniform cells and having excellent appearance, toughness and flexibility. The ethylene resin foamed product comprises an ethylene/α-olefin copolymer having the following properties: the density is in the range of 0.880 to 0.940 g/cm 3 ; the melt flow rate (MFR) at 190° C. under a load of 2.16 kg is in the range of 0.1 to 20 g/10 min; the decane-soluble component fraction (W) at room temperature and the density (d) satisfy the relation W&lt;80×exp(−100(d−0.88))+0.1 in case of MFR≦10 g/10 min and the relation W&lt;80×(MFR-9) 0.26 ×exp(−100(d−0.88))+0.1 in case of MFR&gt;10 g/10 min; and the temperature (TM) at the maximum peak position in the endothermic curve as measured by a differential scanning calorimeter and the density (d) satisfy the relation Tm&lt;400×d−250.

TECHNICAL FIELD

The present invention relates to ethylene resin foamed productscomprising ethylene copolymers, and more particularly to foamed productscontaining uniform cells and having excellent appearance, toughness andheat resistance.

BACKGROUND ART

Ethylene resin foamed products have excellent flexibility and heatinsulating properties, so that they have been hitherto applied tovarious uses as cushioning materials or heat insulating materials. Thetype of a polyethylene resin is selected according to the use purpose ofthe resulting foamed product. For example, when the foamed productrequires flexibility, low-density polyethylene is used, and when thefoamed product requires toughness, linear low-density polyethylene or aresin composition consisting of low-density polyethylene and linearlow-density polyethylene is used (see Japanese Patent Publication No.57334/1986).

The linear low-density polyethylene is a copolymer of ethylene and anα-olefin, and in order to enhance flexibility, a resin produced using anincreased amount of an α-olefin that is a comonomer component is used.In such a resin, however, a low-molecular weight polymer portion inwhich the comonomer component is introduced into the molecular chainsand a high-molecular weight polymer portion in which the comonomercomponent is rarely introduced are present separately from each other,so that a wide scatter of melt viscosity value occurs in the resin tothereby lower foamability of the resin. For example, the expansion ratiodoes not increase, or even if a foamed product having a satisfactoryexpansion ratio is obtained, the product has a problem in appearancesuch as protrusions or depressions, or the product contains both ofextremely large cells and small cells and is broken from the ununiformlyfoamed portion during the forming process.

As tape substrates or sheet substrates used for compress materials oranti-inflammatory analgesic plasters, foamed products of small thicknessare used instead of cloths or flexible synthetic resins, and such tapesubstrates or sheet substrates are required to have flexibility andtoughness (favorable extensibility and tensile strength). As the tapesubstrates or the sheet substrates of this kind, crosslinked foamedproducts comprising a resin composition consisting of an ethylene/vinylacetate copolymer and linear low-density polyethylene have been proposed(Japanese Patent Publication No. 33387/1990). The crosslinked foamedproducts as tape substrates, however, have bad balance betweenflexibility and toughness. If the amount of the ethylene/vinyl acetatecopolymer is increased in order to obtain products of more flexibility,the tensile strength of the products is lowered.

The conventional polyethylene resins are markedly lowered in theviscosity when they are exposed to high temperatures or subjected tomelting, so that crosslinking is generally made to ensureviscoelasticity of such a level as required in the foaming process andto retain the produced cells. For crosslinking the polyethylene resins,various methods such as an irradiation crosslinking method usingionizing radiation, a peroxide crosslinking method in which resinradicals are produced by a peroxide to perform crosslinking,crosslinking method adding a multifunctional monomer in the producedradicals and a crosslinking method by means of silanol condensation(silane crosslinking method) have been industrially carried out.Uncrosslinked polyethylene resin foamed products are industriallyproduced by dispersing or dissolving in a resin a substance that isgasified at ordinary temperature and atmospheric pressure or uponheating, such as carbonic acid gas, methanol, water or flon, andsubjecting the dispersion or the solution to extrusion foaming or batchfoaming.

The conventional resins, however, are difficult to control degree ofcrosslinking, and it is not easy to produce crosslinked foamed productsof certain qualities. Further, when the conventional polyethylene resinsare not crosslinked, the viscosity of the resins is markedly loweredunder the foaming conditions as described above, and hence it is verydifficult to obtain uncrosslinked foamed products. In particular, it isdifficult to produce conventional uncrosslinked polyethylene foamedproducts as continuous sheet products, although it is possible toproduce them as small-area products such as rod or tubular products.

The present invention is intended to solve such problems associated withthe prior art as described above, and it is an object of the inventionto provide ethylene resin foamed products containing uniform cells andhaving excellent appearance, toughness and flexibility.

DISCLOSURE OF THE INVENTION

The ethylene resin foamed product according to the present inventioncomprises an ethylene/α-olefin copolymer which is a copolymer ofethylene and an α-olefin of 3 to 12 carbon atoms and meets the followingrequirements:

(i) the density is in the range of 0.880 to 0.940 g/cm³,

(ii) the melt flow rate (MFR) at 190° C. under a load of 2.16 kg is inthe range of 0.1 to 20 g/10 min,

(iii) the decane-soluble component fraction (W (% by weight)) at roomtemperature and the density (d (g/cm³)) satisfy the following relation

in case of MFR≦10 g/10 min:

W<80×exp(−100(d−0.88))+0.1,

in case of MFR>10 g/10 min:

W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1,

 and

(iv) the temperature (Tm (° C.)) at the maximum peak position in theendothermic curve as measured by a differential scanning calorimeter(DSC) and the density (d (g/cm³)) satisfy the following relation

 Tm<400×d−250.

The ethylene/α-olefin copolymer is desired to further meet, in additionto the requirements (i) to (iv), the following requirements:

(v) the flow index (FI (1/sec)), which is defined as a shear rate atwhich the shear stress of said copolymer in a molten state at 190° C.reaches 2.4×10⁶ dyne/cm², and the melt flow rate (MFR (g/10 min))satisfy the following relation

FI>75×MFR,

 and

(vi) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR(g/10 min)) satisfy the following relation

MT>2.2×MFR^(−0.84).

The ethylene/α-olefin copolymer is also desired to further meet, inaddition to the requirements (i) to (iv), the following requirements:

(vii) the flow index (FI (1/sec)), which is defined as a shear rate atwhich the shear stress of said copolymer in a molten state at 190° C.reaches 2.4×10⁶ dyne/cm², and the melt flow rate (MFR (g/10 min))satisfy the following relation

FI>150×MFR,

 and

(viii) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR(g/10 min)) satisfy the following relation

MT>4.0×MFR^(−0.65).

The ethylene/α-olefin copolymer is also desired to further meet, inaddition to the requirements (i) to (iv), the following requirements:

(ix) the flow index (FI (1/sec)), which is defined as a shear rate atwhich the shear stress of said copolymer in a molten state at 190° C.reaches 2.4×10⁶ dyne/cm², and the melt flow rate (MFR (g/10 min))satisfy the following relation

FI≦75×MFR.

The ethylene/α-olefin copolymer is preferably a copolymer obtained bycopolymerizing ethylene and an α-olefin of 3 to 12 carbon atoms in thepresence of an olefin polymerization catalyst comprising:

(a) a compound of a transition metal of Group IV of the periodic table,which contains a ligand having cyclopentadienyl skeleton, and

(b) an organoaluminum oxy-compound.

The ethylene/α-olefin copolymer mentioned above is favorable forproducing foamed products.

It is preferable that when the ethylene resin foamed product of theinvention is subjected to a temperature rise elution test (TREF), acomponent that is eluted at a temperature of not lower than 100° C. ispresent and the amount of the component that is eluted at a temperatureof not lower than 100° C. is not more than 10% of the whole elutionamount.

The ethylene resin foamed product according to the present inventionpreferably comprises crosslinked polyethylene obtained by crosslinkingthe ethylene/α-olefin copolymer.

BEST MODE FOR CARRYING OUT THE INVENTION

The ethylene resin foamed product according to the invention isdescribed in detail hereinafter.

Ethylene/α-olefin copolymer

The ethylene/α-olefin copolymer for producing an ethylene resin foamedproduct of the invention is a copolymer of ethylene and an α-olefin of 3to 12 carbon atoms.

In the copolymer, constituent units derived from ethylene are desired tobe present in amounts of 55 to 99% by weight, preferably 65 to 98% byweight, more preferably 70 to 96% by weight, and constituent unitsderived from the α-olefin of 3 to 12 carbon atoms are desired to bepresent in amounts of 1 to 45% by weight, preferably 2 to 35% by weight,more preferably 4 to 30% by weight.

Examples of the α-olefins of 3 to 12 carbon atoms include propylene,1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-deceneand 1-dodecene.

The ethylene/α-olefin copolymer meets the following requirements (i) to(iv).

(i) The density of the ethylene/α-olefin copolymer is in the range of0.880 to 0.940 g/cm³, preferably 0.900 to 0.940 g/cm³.

(ii) The melt flow rate (MFR) of the ethylene/α-olefin copolymer is inthe range of 0.1 to 20 g/10 min, preferably 0.3 to 10 g/10 min.

(iii) The n-decane-soluble component fraction (W (% by weight)) in theethylene/α-olefin copolymer at room temperature and the density (d(g/cm³)) of the copolymer satisfy the following relation

in case of MFR≦10 g/10 min:

W<80×exp(−100(d−0.88))+0.1,

preferably W<60×exp(−100(d−0.88))+0.1,

in case of MFR>10 g/10 min:

W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1.

(iv) The temperature (Tm (° C.)) at the maximum peak position in theendothermic curve of the ethylene/α-olefin copolymer as measured by adifferential scanning calorimeter (DSC) and the density (d (g/cm³)) ofthe copolymer satisfy the following relation

Tm<400×d−250,

preferably Tm<450×d−297.

An ethylene resin foamed product produced from the ethylene/α-olefincopolymer meeting the above requirements contains uniform cells and hasexcellent heat resistance.

The ethylene/α-olefin copolymer is desired to further meet the followingrequirements (v) to (vi) in addition to the requirements (i) to (iv).

(v) The flow index (FI (1/sec)), which is defined as a shear rate atwhich the shear stress of the ethylene/α-olefin copolymer in a moltenstate at 190° C. reaches 2.4×10 ⁶ dyne/cm², and the melt flow rate (MFR(g/10 min)) of the copolymer satisfy the following relation

FI>75×MFR,

preferably FI≧150×MFR,

more preferably FI≦250×MFR.

(vi) The melt tension (MT (g)) at 190° C. and the melt flow rate (MFR(g/10 min)) satisfy the following relation

MT>2.2×MFR^(−0.84),

preferably MT>4.0×MFR^(−0.65),

more preferably MT>5.0×MFR^(−0.65).

An ethylene resin foamed product produced from the ethylene/α-olefincopolymer meeting the above requirements contains uniform cells and hasexcellent heat resistance. Moreover, the ethylene resin foamed productis excellent particularly in foam properties when it is in theuncrosslinked state.

The ethylene/α-olefin copolymer is also desired to further meet thefollowing requirements (vii) in addition to the requirements (i) to(iv).

(vii) The flow index (FI (1/sec)), which is defined as a shear rate atwhich the shear stress of said copolymer in a molten state at 190° C.reaches 2.4×10⁶ dyne/cm², and the melt flow rate (MFR (g/10 min))satisfy the following relation

FI≦75×MFR.

An ethylene resin foamed product produced from the ethylene/α-olefincopolymer meeting the above requirements contains uniform cells and hasexcellent heat resistance and tensile properties.

It is desirable that when the ethylene resin foamed product is subjectedto a temperature rise elution test (TREF), a component that is eluted ata temperature of not lower than 100° C. is present and the amount of thecomponent that is eluted at a temperature of not lower than 100° C. isnot more than 10%, preferably 0.5 to 8%, of the whole elution amount.

The olefin polymerization catalyst and the catalyst components aredescribed below.

The ethylene/α-olefin copolymer for use in the invention can be preparedby, for example, copolymerizing ethylene and an α-olefin of 3 to 20carbon atoms in the presence of an olefin polymerization catalystcomprising:

(a) a compound of a transition metal of Group IV of the periodic table,which contains a ligand having cyclopentadienyl skeleton,

(b) an organoaluminum oxy-compound,

(c) a carrier, and optionally

(d) an organoaluminum compound.

(a) Transition Metal Compound

The olefin polymerization catalyst and the catalyst components aredescribed below.

The compound (a) of a transition metal of Group IV of the periodictable, which contains a ligand having cyclopentadienyl skeleton,(sometimes referred to as a “component (a)” hereinafter) is specificallya transition metal compound represented by the following formula (I) or(II).

MKL¹ _(x−2)  (I)

wherein M is a transition metal atom selected from Group IVB of theperiodic table; K and L¹ are each a ligand coordinated to the transitionmetal atom; the ligand K is a bidentate ligand wherein the same ordifferent groups selected from indenyl groups, substituted indenylgroups and their partially hydrogenated products are linked through alower alkylene group; the ligand L¹ is a hydrocarbon group of 1 to 12carbon atoms, an alkoxy group, an aryloxy group, a halogen atom, atrialkylsilyl group or a hydrogen atom; and x is a valence of thetransition metal atom M.

ML² _(x)  (II)

wherein M is a transition metal selected from Group IV of the periodictable; L² is a ligand coordinated to the transition metal atom, at leasttwo ligands L² are each a substituted cyclopentadienyl group having 2 to5 substituents selected from methyl and ethyl, and the ligand L² otherthan the substituted cyclopentadienyl group is a hydrocarbon group of 1to 12 carbon atoms, an alkoxy group, an aryloxy group, a halogen atom, atrialkylsilyl group or a hydrogen atom; and x is a valence of thetransition metal atom M.

In the formula (I), M is a transition metal atom selected from Group IVof the periodic table, specifically zirconium, titanium or hafnium,preferably zirconium.

K is a ligand coordinated to the transition metal atom, and is abidentate ligand wherein the same or different groups selected fromindenyl groups, substituted indenyl groups and partially hydrogenatedproducts of indenyl groups and substituted indenyl groups are linkedthrough a lower alkylene group.

Examples of such ligands include an ethylenebisindenyl group, anethylenebis(4,5,6,7-tetrahydro-1-indenyl) group, anethylenebis(4-methyl-1-indenyl) group, anethylenebis(5-methyl-1-indenyl) group, anethylenebis(6-methyl-1-indenyl) group and anethylenebis(7-methyl-1-indenyl) group.

L¹ is a hydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, anaryloxy group, a halogen atom, a trialkylsilyl group or a hydrogen atom.

Examples of the hydrocarbon groups of 1 to 12 carbon atoms include alkylgroups, cycloalkyl groups, aryl groups and aralkyl groups. Morespecifically, here can be mentioned alkyl groups, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl,hexyl, octyl, 2-ethylhexyl and decyl; cycloalkyl groups, such ascyclopentyl and cyclohexyl; aryl groups, such as phenyl and tolyl; andaralkyl groups, such as benzyl and neophyl.

Examples of the alkoxy groups include methoxy, ethoxy, n-propoxy,isopropoxy, n-butoxy, isobutoxy, sec-butoxy, t-butoxy, pentoxy, hexoxyand octoxy.

An example of the aryloxy group is phenoxy.

The halogen atom is fluorine, chlorine, bromine or iodine.

Examples of the trialkylsilyl groups include trimethylsilyl,triethylsilyl and triphenylsilyl.

Examples of the transition metal compounds represented by the formula(I) include:

ethylenebis(indenyl)zirconium dichloride,

ethylenebis(4-methyl-1-indenyl)zirconium dichloride,

ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride,

ethylenebis(5-methyl-1-indenyl)zirconium dichloride,

ethylenebis(6-methyl-1-indenyl)zirconium dichloride,

ethylenebis(7-methyl-1-indenyl)zirconium dichloride,

ethylenebis(4-methyl-1-indenyl)zirconium dibromide,

ethylenebis(4-methyl-1-indenyl)zirconium methoxychloride,

ethylenebis(4-methyl-1-indenyl)zirconium ethoxychloride,

ethylenebis(4-methyl-1-indenyl)zirconium butoxychloride,

ethylenebis(4-methyl-1-indenyl)zirconium methoxide,

ethylenebis(4-methyl-1-indenyl)zirconium methylchloride,

ethylenebis(4-methyl-1-indenyl)zirconium dimethyl,

ethylenebis(4-methyl-1-indenyl)zirconium benzylchloride,

ethylenebis(4-methyl-1-indenyl)zirconium dibenzyl,

ethylenebis(4-methyl-1-indenyl)zirconium phenylchloride, and

ethylenebis(4-methyl-1-indenyl)zirconium hydride chloride.

In the present invention, transition metal compounds wherein a zirconiummetal is replaced with a titanium metal or a hafnium metal in theabove-mentioned zirconium compounds are also employable.

Of the above transition metal compounds represented by the formula (I),particularly preferable are:

ethylenebis(indenyl)zirconium dichloride,

ethylenebis(4-methyl-1-indenyl)zirconium dichloride, and

ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride.

In the formula (II), M is a transition metal atom selected from Group IVof the periodic table, specifically zirconium, titanium or hafnium,preferably zirconium.

L² is a ligand coordinated to the transition metal atom M, and at leasttwo ligands L² are each a substituted cyclopentadienyl group having 2 to5 substituents selected from methyl and ethyl. The ligands may be thesame or different. The substituted cyclopentadienyl group is asubstituted cyclopentadienyl group having two or more substituents,preferably a cyclopentadienyl group having 2 to 3 substituents, morepreferably a di-substituted cyclopentadienyl group, particularlypreferably a 1,3-substituted cyclopentadienyl group. The substituentsmay be the same or different.

In the formula (II), the ligand L² other than the substitutedcyclopentadienyl group coordinated to the transition metal atom M is ahydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, an aryloxygroup, a halogen atom, a trialkylsilyl group or a hydrogen atom.

Examples of the transition metal compounds represented by the formula(II) include:

bis(cyclopentadienyl)zirconium dichloride,

bis(methylcyclopentadienyl)zirconium dichloride,

bis(ethylcyclopentadienyl)zirconium dichloride,

bis(n-propylcyclopentadienyl)zirconium dichloride,

bis(n-butylcyclopentadienyl)zirconium dichloride,

bis(n-hexylcyclopentadienyl)zirconium dichloride,

bis(methyl-n-propylcyclopentadienyl)zirconium dichloride,

bis(methyl-n-butylcyclopentadienyl)zirconium dichloride,

bis(dimethyl-n-butylcyclopentadienyl)zirconium dichloride,

bis(n-butylcyclopentadienyl)zirconium dibromide,

bis(n-butylcyclopentadienyl)zirconium methoxychloride,

bis(n-butylcyclopentadienyl)zirconium ethoxychloride,

bis(n-butylcyclopentadienyl)zirconium butoxychloride,

bis(n-butylcyclopentadienyl)zirconium ethoxide,

bis(n-butylcyclopentadienyl)zirconium methylchloride,

bis(n-butylcyclopentadienyl)zirconium dimethyl,

bis(n-butylcyclopentadienyl)zirconium benzylchloride,

bis(n-butylcyclopentadienyl)zirconium dibenzyl,

bis(n-butylcyclopentadienyl)zirconium phenylchloride,

bis(n-butylcyclopentadienyl)zirconium hydride chloride,

bis(dimethylcyclopentadienyl)zirconium dichloride,

bis(diethylcyclopentadienyl)zirconium dichloride,

bis(methylethylcyclopentadienyl)zirconium dichloride,

bis(dimethylethylcyclopentadienyl)zirconium dichloride,

bis(dimethylcyclopentadienyl)zirconium dibromide,

bis(dimethylcyclopentadienyl)zirconium methoxychloride,

bis(dimethylcyclopentadienyl)zirconium ethoxychloride,

bis(dimethylcyclopentadienyl)zirconium butoxychloride,

bis(dimethylcyclopentadienyl)zirconium diethoxide,

bis(dimethylcyclopentadienyl)zirconium methylchloride,

bis(dimethylcyclopentadienyl)zirconium dimethyl,

bis(dimethylcyclopentadienyl)zirconium benzylchloride,

bis(dimethylcyclopentadienyl)zirconium dibenzyl,

bis(dimethylcyclopentadienyl)zirconium phenylchloride, and

bis(dimethylcyclopentadienyl)zirconium hydride chloride.

In the above examples, the di-substituted cyclopentadienyl rings include1,2- and 1,3-substituted cyclopentadienyl rings. In the presentinvention, transition metal compounds wherein a zirconium metal isreplaced with a titanium metal or a hafnium metal in the above-mentionedzirconium compounds are also employable.

Of the above transition metal compounds represented by the formula (I),particularly preferable are:

bis(n-propylcyclopentadienyl)zirconium dichloride,

bis(n-butylcyclopentadienyl)zirconium dichloride,

bis(1-methyl-3-n-propylcyclopentadienyl)zirconium dichloride,

bis)1-methyl-3-n-butylcyclopentadienyl)zirconium dichloride,

bis(1,3-dimethylcyclopentadienyl)zirconium dichloride,

bis(1,3-diethylcyclopentadienyl)zirconium dichloride, and

bis)1-methyl-3-ethylcyclopentadienyl)zirconium dichloride.

(b) Organoaluminum oxy-compound

The organoaluminum oxy-compound (b) is described below.

The organoaluminum oxy-compound (b) (sometimes referred to as a“component (b)” hereinafter) for use in the invention may bebenzene-soluble aluminoxane hitherto known or such a benzene-insolubleorganoaluminum oxy-compound as disclosed in Japanese Patent Laid-OpenPublication No. 276807/1990.

The aluminoxane can be prepared by, for example, the followingprocesses.

(1) An organoaluminum compound such as trialkylaluminum is added to ahydrocarbon medium suspension of a compound containing adsorption wateror a salt containing water of crystallization, e.g., magnesium chloridehydrate, copper sulfate hydrate, aluminum sulfate hydrate, nickelsulfate hydrate or cerous chloride hydrate, to allow the organoaluminumcompound to react with the adsorption water or the water ofcrystallization, and the aluminoxane is recovered as a hydrocarbonsolution.

(2) Water, ice or water vapor is allowed to directly act on anorganoaluminum compound such as trialkylaluminum in a medium such asbenzene, toluene, ethyl ether or tetrahydrofuran, and the aluminoxane isrecovered as a hydrocarbon solution.

(3) An organotin oxide such as dimethyltin oxide or dibutyltin oxide isallowed to react with an organoaluminum compound such astrialkylaluminum in a medium such as decane, benzene or toluene.

The aluminoxane may contain a small amount of an organometalliccomponent. It is possible that the solvent or the unreactedorganoaluminum compound is distilled off from the recovered solution ofaluminoxane and the remainder is redissolved in a solvent.

Examples of the organoaluminum compounds used for preparing thealuminoxane include:

trialkylaluminums, such as trimethylaluminum, triethylaluminum,tripropylaluminum, triisopropylaluminum, tri-n-butylaluminum,triisobutylaluminum, tri-sec-butylaluminum, tri-tert-butylaluminum,tripentylaluminum, trihexylaluminum, trioctylaluminum andtridecylaluminum;

tricycloalkylaluminums, such as tricyclohexylaluminum andtricyclooctylaluminum;

dialkylaluminum halides, such as dimethylaluminum chloride,diethylaluminum chloride, diethylaluminum bromide and diisobutylaluminumchloride;

dialkylaluminum hydrides, such as diethylaluminum hydride anddiisobutylaluminum hydride;

dialkylaluminum alkoxides, such as dimethylaluminum methoxide anddiethylaluminum ethoxide; and

dialkylaluminum aryloxides, such as diethylaluminum phenoxide.

Of these, trialkylaluminums and trialkylaluminums are particularlypreferable.

Also employable as the organoaluminum compound is isoprenylaluminumrepresented by the following formula:

(i-C₄H₉)_(x)Al_(y)(C₅H₁₀)z

wherein x, y, z are each a positive number, and z≧2x.

The organoaluminum compounds mentioned above are used singly or incombination.

Examples of the solvents used for preparing the aluminoxane includearomatic hydrocarbons, such as benzene, toluene, xylene, cumene andcymene; aliphatic hydrocarbons, such as pentane, hexane, heptane,octane, decane, dodecane, hexadecane and octadecane; alicyclichydrocarbons, such as cyclopentane, cyclohexane, cyclooctane andmethylcyclopentane; petroleum fractions, such as gasoline, kerosine andgas oil; and halogenated products of these aromatic, aliphatic andalicyclic hydrocarbons, particularly chlorinated or brominated productsthereof. Also employable are ethers such as ethyl ether andtetrahydrofuran. Of the solvents, aromatic hydrocarbons are particularlypreferable.

The benzene-insoluble organoaluminum oxy-compound contains not more than10% (in terms of Al atom), preferably not more than 5%, particularlypreferably not more than 2%, of an Al component that is soluble inbenzene at 60° C., and is insoluble or sparingly soluble in benzene.

The solubility of the organoaluminum oxy-compound in benzene can bedetermined in the following manner. The organoaluminum oxy-compound inan amount corresponding to 100 mg·atom of Al is suspended in 100 ml ofbenzene, and they are mixed a 60° C. for 6 hours with stirring. Then,the mixture is subjected to hot filtration at 60° C. using a jacketedG-5 glass filter, and the solid separated on the filter is washed fourtimes with 50 ml of benzene at 60° C. to obtain filtrates. The amount(×mmol) of Al atom present in all of the filtrates is measured todetermine the solubility (×%)

Carrier (c)

The carrier (c) for use in the invention is an inorganic or organiccompound of granular or particulate solid having a particle diameter of10 to 300 μm, preferably 20 to 200 μm. The inorganic carrier ispreferably a porous oxide, and examples thereof include SiO₂, Al₂O₃,MgO, ZrO₂, TiO₂, B₂O₃, CaO, ZnO, BaO, ThO₂, and mixtures thereof such asSiO₂—MgO, SiO₂—Al₂O₃, SiO₂—TiO₂, SiO₂—V₂O₅, SiO₂—Cr₂O₃ andSiO₂—TiO₂—MgO. Of these, preferable are oxides containing at least onecomponent selected from the group consisting of SiO₂ and Al₂O₃ as theirmajor component.

The inorganic oxides may contain small amounts of carbonate, sulfate,nitrate and oxide components, such as Na₂CO₃, K₂CO₃, CaCO₃, MgCO₃,Na₂SO₄, Al₂(SO₄)₃, BaSO₄, KNO₃, Mg(NO₃)₂, Al(NO₃)₃, Na₂O, K₂O and Li₂O.

Although the carriers (c) differ in the properties depending upon thetype and the preparation process, the carrier preferably used in theinvention is desired to have a specific surface area of 50 to 1000 m²/g,preferably 100 to 700 m²/g, and a pore volume of 0.3 to 2.5 cm²/g. Thecarrier is used after calcined at a temperature of 100 to 1000° C.,preferably 150 to 700° C., if necessary.

Also employable as the carrier in the invention is an organic compoundof granular or particulate solid having a particle diameter of 10 to 300μm. Examples of such organic compounds include (co)polymers producedusing an α-olefin of 2 to 14 carbon atoms such as ethylene, propylene,1-butene or 4-methyl-1-pentene as a main component, and (co)polymersproduced using vinylcyclohexane or styrene as a main component.

In the present invention, the olefin polymerization catalyst used forpreparing the ethylene/α-olefin copolymer is formed from the component(a), the component (b) and the carrier (c), but an organoaluminumcompound (d) may also be used, if necessary.

(d) Organoaluminum Compound

The organoaluminum compound (d) (sometimes referred to as a “component(d)” hereinafter) that is optionally used is, for example, anorganoaluminum compound represented by the following formula (III):

 R¹ _(n)AlX_(3−n)  (III)

wherein R¹ is a hydrocarbon group of 1 to 12 carbon atoms, X is ahalogen atom or a hydrogen atom, and n is 1 to 3.

In the formula (III), R¹ is a hydrocarbon group of 1 to 12 carbon atoms,e.g., an alkyl group, a cycloalkyl group or an aryl group. Examples ofsuch groups include methyl, ethyl, n-propyl, isopropyl, isobutyl,pentyl, hexyl, octyl, cyclopentyl, cyclohexyl, phenyl and tolyl.

Examples of such organoaluminum compounds include:

trialkylaluminums, such as trimethylaluminum, triethylaluminum,triisopropylaluminum, triisobutylaluminum, trioctylaluminum andtri-2-ethylhexylaluminum;

alkenylaluminums, such as isoprenylaluminum;

dialkylaluminum halides, such as dimethylaluminum chloride,diethylaluminum chloride, diisopropylaluminum chloride,diisobutylaluminum chloride and dimethylaluminum bromide;

alkylaluminum sesquihalides, such as methylaluminum sesquichloride,ethylaluminum sesquichloride, isopropylaluminum sesquichloride,butylaluminum sesquichloride and ethylaluminum sesquibromide;

alkylaluminum dihalides, such as methylaluminum dichloride,ethylaluminum dichloride, isopropylaluminum dichloride and ethylaluminumdibromide; and

alkylaluminum hydrides, such as diethylaluminum hydride anddiisobutylaluminum hydride.

Also employable as the organoaluminum compound (d) is a compoundrepresented by the following formula (IV):

R¹ _(n)AlY_(3−n)  (IV)

wherein R¹ is the same hydrocarbon as indicated by R¹ in the formula(III); Y is —OR₂ group, —OSiR³ ₃ group, —OAlR⁴ ₂ group, —NR⁵ ₂ group,—SiR⁶ ₃ group or —N(R⁷)AlR⁸ ₂ group; n is 1 to 2; R², R³, R⁴ and R⁸ areeach methyl, ethyl, isopropyl, isobutyl, cyclohexyl, phenyl or the like;R⁵ is hydrogen, methyl, ethyl, isopropyl, phenyl, trimethylsilyl or thelike; and R⁶ and R⁷ are each methyl, ethyl or the like.

Examples of such organoaluminum compounds include:

(1) compounds represented by R¹ _(n)Al(OR²)_(3−n), such asdimethylaluminum methoxide, diethylaluminum ethoxide anddiisobutylalum-num methoxide;

(2) compounds represented by R¹ _(n)Al(OSiR³ ₃)_(3−n), such asEt₂Al(OSiMe₃), (iso-Bu)₂Al(OSiMe₃) and (iso-Bu)₂Al(OSiEt₃);

(3) compounds represented by R¹ _(n)Al(OAlR⁴ ₂)_(3−n), such asEt₂AlOAlEt₂ and (iso-Bu)₂AlOAl(iso-Bu)₂;

(4) compounds represented by R¹ _(n)Al(NR⁵ ₂)_(3−n), such as Me₂AlNEt₂,Et₂AlNHMe, Me₂AlNHEt, Et₂AlN(SiMe₃)₂ and (iso-Bu)₂AlN(SiMe₃)₂;

(5) compounds represented by R¹ _(n)Al(SiR⁶ ₃)_(3−n), such as(iso-Bu)₂AlSiMe₃; and

(6) compounds represented by R¹ _(n)Al(N(R⁷)AlR⁸ ₂)_(3−n), such asEt₂AlN(Me)AlEt₂ and (iso-Bu)₂AlN(Et)Al(iso-Bu)₂.

Of the organoaluminum compounds represented by the formulas (III) and(IV), preferable are compounds represented by the formulas R¹ ₃Al, R¹_(n)Al(OR²)_(3−n) and R¹ _(n)Al(OAlR⁴ ₂)_(3−n), and particularlypreferable are compounds of said formulas wherein R¹ is an isoalkylgroup and n is 2.

Process for the Preparation of Catalyst

n the preparation of the ethylene/α-olefin copolymer for use in theinvention, a catalyst prepared by contacting the component (a), thecomponent (b), the carrier (c), and if necessary, the component (d) withone another is employed. Although the components may be contacted in anyorder, it is preferable to contact the carrier (c) with the component(b), then with the component (a), and then if necessary, with thecomponent (d).

The contact of the components can be carried out in an inert hydrocarbonsolvent. Examples of the inert hydrocarbon media used for preparing thecatalyst include aliphatic hydrocarbons, such as propane, butane,pentane, hexane, heptane, octane, decane, dodecane and kerosine;alicyclic hydrocarbons, such as cyclopentane, cyclohexane andmethylcyclopentane; aromatic hydrocarbons, such as benzene, toluene andxylene; halogenated hydrocarbons, such as ethylene chloride,chlorobenzene and dichloromethane; and mixtures of these hydrocarbons.

In the contact of the component (a), the component (b), the carrier (c)and the component (d) optionally used, the component (a) is used in anamount of usually 5×10⁻⁶ to 5×10⁻⁴ mol, preferably 10⁻⁵ to 2×10⁻⁴ mol,based on 1 g of the carrier (c), and the concentration of the component(a) is in the range of about 10⁻⁴ to 2×10⁻² mol/l, preferably 2×10⁻⁴ to10⁻² mol/l. The atomic ratio (Al/transition metal) of aluminum in thecomponent (b) to the transition metal in the component (a) is in therange of usually 10 to 500, preferably 20 to 200. The atomic ratio((Al-d)/(Al-b)) of an aluminum atom (Al-d) in the component (d)optionally used to an aluminum atom (Al-b) in the component (b) is inthe range of usually 0.02 to 3, preferably 0.05 to 1.5. In the contactof the component (a), the component (b), the carrier (c) and thecomponent (d) optionally used, the mixing temperature is in the range ofusually −50 to 150° C., preferably −20 to 120° C., and the contact timeis in the range of 1 minute to 50 hours, preferably 10 minutes to 25hours.

In the olefin polymerization catalyst obtained as above, the transitionmetal atom derived from the component (a) is desirably supported in anamount of 5×10⁻⁶ to 5×10⁻⁴ g·atom, preferably 10⁻⁵ to 2×10⁻⁴ g·atom,based on 1 g of the carrier (c), and the aluminum atom derived from thecomponent (b) and the component (d) is desirably supported in an amountof 10⁻³ to 5×10⁻² g·atom, preferably 2×10⁻³ to 2×10⁻² g·atom, based on 1g of the carrier (c).

The catalyst used for preparing the ethylene/α-olefin copolymer may be aprepolymerized catalyst obtained by prepolymerizing an olefin in thepresence of the component (a), the component (b), the carrier (c) andthe component (d) optionally used. The prepolymerization can be carriedout by introducing an olefin into an inert hydrocarbon solvent in thepresence of the component (a), the component (b), the carrier (c) andthe component (d) optionally used.

Examples of the olefins used in the prepolymerization include ethyleneand α-olefins of 3 to 20 carbon atoms, such as propylene, 1-butene,1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodeceneand 1-tetradecene. Of these, particularly preferable is ethylene or acombination of ethylene and an α-olefin, that is used in thepolymerization.

In the prepolymerization, the component (a) is used in an amount ofusually 10⁻⁶ to 2×10⁻² mol/l, preferably 5×10⁻⁵ to 10⁻² mol/l, and thecomponent (a) is used in an amount of usually 5×10⁻⁶ to 5×10⁻⁴ mol,preferably 10⁻⁵ to 2×10⁻⁴ mol, based on 1 g of the carrier (c). Theatomic ratio (Al/transition metal) of aluminum in the component (b) tothe transition metal in the component (a) is in the range of usually 10to 500, preferably 20 to 200. The atomic ratio ((Al-d)/(Al-b)) of analuminum atom (Al-d) in the component (d) optionally used to an aluminumatom (Al-b) in the component (b) is in the range of usually 0.02 to 3,preferably 0.05 to 1.5. The prepolymerization temperature is in therange of −20 to 80° C., preferably 0 to 60° C., and theprepolymerization time is in the range of 0.5 to 100 hours, preferablyabout 1 to 50 hours.

The prepolymerized catalyst is prepared by, for example, the followingprocess. The carrier (c) is suspended in an inert hydrocarbon to give asuspension. To the suspension, the organoaluminum oxy-compound(component (b)) is added, and they are reacted for a given period oftime. Then, the supernatant liquid is removed, and the resulting solidcomponent is resuspended in an inert hydrocarbon. To the system, thetransition metal compound (component (a)) is added, and the reaction isconducted for a given period of time. Then, the supernatant liquid isremoved to obtain a solid catalyst component. Subsequently, to an inerthydrocarbon containing the organoaluminum compound (component (d)), theabove-obtained solid catalyst component is added and an olefin isfurther introduced, whereby a prepolymerized catalyst is obtained.

It is desirable that the amount of an olefin polymer produced in theprepolymerization is in the range of 0.1 to 500 g, preferably 0.2 to 300g, more preferably 0.5 to 200 g, based on 1 g of the carrier (c). In theprepolymerized catalyst, the component (a) is desirably supported in anamount of about 5×10⁻⁶ to 5×10⁻⁴ g·atom, preferably 10⁻⁵ to 2×10⁻⁴g·atom, in terms of the transition metal atom, based on 1 g of thecarrier (c), and the aluminum atom (Al) derived from the component (b)and the component (d) is desirably supported in such an amount that themolar ratio (Al/M) of the aluminum atom (Al) to the transition metalatom (M) derived from the component (a) becomes 5 to 200, preferably 10to 150.

The prepolymerization can be carried out by any of batchwise andcontinuous processes, and can be carried out under reduced pressure, atatmospheric pressure or under pressure. In the prepolymerization, it isdesirable to produce a prepolymer having an intrinsic viscosity (η), asmeasured in decalin at 135° C., of 0.2 to 7 dl/g, preferably 0.5 to 5dl/g, by allowing hydrogen to be present in the system.

The ethylene/α-olefin copolymer for use in the invention is obtained bycopolymerizing ethylene and an α-olefin of 3 to 20 carbon atoms, such aspropylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene,1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or1-eicosene, in the presence of the olefin polymerization catalyst or theprepolymerized catalyst described above.

Polymerization Process

In the present invention, the copolymerization of ethylene and anα-olefin is carried out in a gas phase or a liquid phase of slurry. Inthe slurry polymerization, an inert hydrocarbon may be used as asolvent, or the olefin itself may be used as a solvent.

Examples of the inert hydrocarbon solvents used in the slurrypolymerization include aliphatic hydrocarbons, such as butane,isobutane, pentane, hexane, octane, decane, dodecane, hexadecane andoctadecane; alicyclic hydrocarbons, such as cyclopentane,methylcyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbons,such as benzene, toluene and xylene; and petroleum fractions, such asgasoline, kerosine and gas oil. Of the inert hydrocarbon media,preferable are aliphatic hydrocarbons, alicyclic hydrocarbons andpetroleum fractions.

When the copolymerization is carried out as slurry polymerization or gasphase polymerization, the olefin polymerization catalyst or theprepolymerized catalyst is desirably used in an amount of usually 10⁻⁸to 10⁻³ g·atom/l, preferably 10⁻⁷ to 10⁻⁴ g·atom/l, in terms of aconcentration of the transition metal atom in the polymerizationreaction system.

In the polymerization, an organoaluminum oxy-compound similar to thecomponent (b) and/or the organoaluminum compound (d) may be added. Inthis case, the atomic ratio (Al/M) of an aluminum atom (Al) derived fromthe organoaluminum oxy-compound and the organoaluminum compound to thetransition metal atom (M) derived from the transition metal compound (a)is in the range of 5 to 300, preferably 10 to 200, more preferably 15 to150.

When the slurry polymerization is conducted, the polymerizationtemperature is in the range of usually −50 to 100° C., preferably 0 to90° C. When the gas phase polymerization is conducted, thepolymerization temperature is in the range of usually 0 to 120° C.,preferably 20 to 100° C.

The polymerization pressure is in the range of usually atmosphericpressure to 100 kg/cm², preferably 2 to 50 kg/cm². The polymerizationcan be carried out by any of batchwise, semi-continuous and continuousprocesses.

It is possible to conduct polymerization in two or more stages underdifferent reaction conditions.

Process for the Production of Foamed Product

The ethylene resin foamed product according to the invention is producedby mixing the ethylene/α-olefin copolymer with a blowing agent, heatingthe mixture or reducing the pressure and thereby gasifying the blowingagent or generating a decomposition gas to produce cells in the resinmolded product.

Examples of the processes for producing the ethylene resin foamedproduct of the invention include the following ones.

(1) Extrusion Foaming Process

The ethylene/α-olefin copolymer is fed to a hopper of an extruder. Whenthe copolymer is extruded at a temperature in the vicinity of a meltingpoint of the resin, a physical blowing agent is forced into the extruderthrough a forcing hole provided midway in the extruder and the resin isextruded from an extruder die of desired shape, whereby a foamed productcan be continuously obtained. Examples of the physical blowing agentsinclude volatile blowing agents, such as flon, butane, pentane, hexaneand cyclohexane; and inorganic gas type blowing agents, such asnitrogen, air, water and carbonic acid gas. In the extrusion foaming, acell nucleating agent such as calcium carbonate, talc, clay or magnesiumoxide may be added.

The physical blowing agent is used in an amount of usually 5 to 60 partsby weight, preferably 10 to 50 parts by weight, based on 100 parts byweight of the specific ethylene/α-olefin copolymer. If the amount of thephysical blowing agent is too small, the foam properties of the foamedproduct are lowered. On the other hand, if the amount thereof is toolarge, the strength of the foamed product is lowered.

(2) Foaming Process Using Thermal Decomposition Type Blowing Agent

The ethylene/α-olefin copolymer, a thermal decomposition type organicblowing agent such as azodicarbonamide, and if desired, other additivesand a thermoplastic resin are melt kneaded by a kneading device, such asuniaxial extruder, twin-screw extruder, Banbury mixer, kneader mixer orroll, at a temperature lower than the decomposition temperature of thethermal decomposition type blowing agent, to prepare a foaming resincomposition, and the resin composition is generally molded into a sheet.Then, the sheet is heated to a temperature of not lower than thedecomposition temperature of the blowing agent, whereby a foamed productcan be obtained.

The thermal decomposition type organic blowing agent is used in anamount of usually 1 to 50 parts by weight, preferably 4 to 25 parts byweight, based on 100 parts by weight of the specific ethylene/α-olefincopolymer. If the amount of the thermal decomposition type organicblowing agent is too small, the foam properties of the foamed productare lowered. On the other hand, if the amount thereof is too large, thestrength of the foamed product is lowered.

(3) Foaming Process Using Pressure Vessel

The ethylene/α-olefin copolymer is molded into a sheet or a block bymeans of a pressing machine or an extruder. Then, the molded product isplaced in a pressure vessel, and a physical blowing agent issufficiently dissolved in the resin. Then, the pressure is reduced,whereby a foamed product can be produced. It is also possible that apressure vessel in which the molded product has been placed is filledwith a physical blowing agent at ordinary room temperature, then thepressure in the vessel is increased and then reduced, and the moldedproduct is taken out of the vessel and heated in an oil bath, an oven orthe like to foam the molded product.

If the ethylene/α-olefin copolymer is previously crosslinked, anethylene resin foamed product comprising crosslinked polyethylene can beobtained.

Examples of general crosslinking methods include crosslinking by thermaldecomposition of a peroxide radical initiator having been mixed with theresin, crosslinking by irradiation with ionizing radiation, crosslinkingby irradiation with ionizing radiation in the presence of apolyfunctional monomer and silane crosslinking.

In order to obtain a crosslinked foamed product through such methods,the ethylene/α-olefin copolymer, a thermal decomposition type organicblowing agent, a polyfunctional monomer as a crosslinking assistant andother additives are melt kneaded at a temperature lower than thedecomposition temperature of the thermal decomposition type blowingagent and molded into a sheet. The foaming resin composition sheet thusobtained is irradiated with ionizing radiation in a prescribed dose tocrosslink the ethylene/α-olefin copolymer. Then, the crosslinked sheetis heated to a temperature of not lower than the decompositiontemperature of the blowing agent to foam the sheet. Examples of theionizing radiation include α-rays, β-rays, γ-rays and electron rays.Instead of the crosslinking by irradiation with ionizing radiation,peroxide crosslinking or silane crosslinking can be carried out.

In the present invention, additives, such as weathering stabilizer, heatstabilizer, antistatic agent, anti-slip agent, anti-blocking agent,anti-fogging agent, lubricant, pigment, dye, nucleating agent,plasticizer, anti-aging agent, hydrochloric acid absorbent andantioxidant, may be optionally added to the ethylene/α-olefin copolymerin amounts not detrimental to the object of the present invention.Further, other polymer compounds can be blended in small amounts withoutdeparting from the spirit of the present invention.

EFFECT OF THE INVENTION

According to the present invention, a foamed product comprising anethylene/α-olefin copolymer and having excellent flexibility, toughnessand formability can be provided. The uncrosslinked foamed product isexcellent also in recycling properties.

EXAMPLE

The present invention is further described with reference to thefollowing examples, but it should be construed that the invention is inno way limited to those examples.

In the examples and the comparative examples, properties of the foamedproducts were evaluated in the following manner.

(1) Granulation of Ethylene/α-olefin Copolymer

To 100 parts by weight of an ethylene/α-olefin copolymer powder obtainedby gas phase polymerization, 0.05 part by weight oftri(2,4-di-t-butylphenyl)phosphate as a secondary antioxidant, 0.1 partby weight of n-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butylphenyl)propionateas a heat stabilizer and 0.05 part by weight of calcium stearate as ahydrochloric acid absorbent were added. Then, the mixture was meltextruded by a conical tapered twin-screw extruder manufactured by HaakeCo. at a preset temperature of 180° C. to prepare granulation pellets.

(2) Density

Strands obtained in the measurement of melt flow rate (MFR) at 190° C.under a load of 2.16 kg were heat treated at 120° C. for 1 hour and thenslowly cooled to room temperature over a period of 1 hour. Then, thedensity was measured by a density gradient tube.

(3) Composition of Copolymer

Composition of a copolymer was determined by ¹³C-NMR. That is, in a testLube having a diameter of 10 mm, a copolymer powder of about 200 mg washomogeneously dissolved in 1 ml of hexachlorobutadiene to give a sample,and a ¹³C-NMR spectrum of the sample was measured under the conditionsof a measuring temperature of 120° C., a measuring frequency of 25.05MHz, a spectral width of 1500 Hz, a pulse repetition time of 4.2 sec anda pulse width of 6 μsec, to determine composition of the copolymer.

(4) Melt Flow Fate (MFR)

Using granulation pellets of a copolymer, the melt flow rate wasmeasured in accordance with ASTM D1238-65T under the conditions of atemperature of 190° C. and a load of 2.16 kg.

(5) Molecular Weight Distribution (Mw/Mn)

The molecular weight distribution was measured by Waters GPC ModelALC-GPC-150C. The measurement was carried out at a temperature of 140°C. using a column of PSK-GMH-HT manufactured by Toyo Soda K.K. and usinga solvent of orthodichlorobenzene (ODCB).

(6) Maximum Peak Temperature (Tm) Measured by DSC

The temperature (Tm) at the maximum peak position in the endothermiccurve was determined in the following manner using an apparatus of DSC-7Model manufactured by Perkin Elmer Co. A sample of about 5 mg was placedin an aluminum pan, heated up to 200° C. at a rate or 10° C./min, heldat 200° C. for 5 minutes, cooled to room temperature at a rate of 10°C./min and then heated at a rate of 10° C./min to give an endothermiccurve, from which the temperature at the maximum peak position wasfound.

(7) n-Decane-soluble Component Fraction (W)

The amount of a n-decane-soluble component in an ethylene/α-olefincopolymer was measured by a method comprising adding about 3 g of thecopolymer to 450 ml of n-decane, dissolving the copolymer at 145° C.,cooling the resulting solution to 23° C., removing a n-decane-insolublecomponent by filtration and recovering a n-decane-soluble component fromthe filtrate.

The n-decane-soluble component fraction is defined as follows.

W (%)=Weight of n-decane-soluble component/(Weight of n-decane-insolubleand soluble components)×100

(8) Melt Tension (MT)

The melt tension was determined by measuring a stress given when amolten polymer was drawn at a constant rate. That is, granulationpellets of a copolymer were used as test samples, and the measurementwas carried out using a MT measuring device manufactured by Toyo SeikiSeisakusho under the conditions of a resin temperature of 190° C., anextrusion temperature of 15 mm/min, a take-up rate of 10 to 20 m/min, anozzle diameter of 2.09 mm and a nozzle length of 8 mm.

(9) Flow Index (FI)

The flow index (FI) is defined as a shear rate at which the shear stressreaches 2.4×10⁶ dyne/cm² at 190° C. The flow index (FI) was determinedby extruding a resin from a capillary with changing a shear rate andmeasuring a stress at each shear rate. That is, the measurement wascarried out using the same sample as in the MT measurement and using acapillary type property tester manufactured by Toyo Seiki Seisakushounder the conditions of a resin temperature of 190° C. and a shearstress range of about 5×10⁴ to 3×10⁶ dyne/cm².

In this measurement, the diameter of a nozzle (capillary) was changed asfollows according to the MFR (g/10 min) of the resin to be measured.

MFR>20: 0.5 mm

20≧MFR>3: 1.0 mm

3≧MFR>0.8: 2.0 mm

0.8≧MFR: 3.0 mm

(10) Temperature Rise Elution Properties (TREF)

A sample solution was introduced into a column at 140° C., then cooledto 25° C. at a cooling rate of 10° C./hr and heated at a heating rate of15° C./hr to detect, on the online system, components having beencontinuously eluted at a constant flow rate of 1.0 ml.

This test was carried out using a column of 2.14 cm (diameter)×15 cm,glass beads having a diameter of 100 μm as packing andorthodichlorobenzene as a solvent under the test conditions of a sampleconcentration of 200 mg/40 ml-orthodichlorobenzene and a pour of 7.5 ml.

(11) Heat Resistance

A foamed sheet was cut into a size of 50×50 mm, and thereto was applieda load of 80 g/cm² at 80° C. to measure a thickness T₀ of the sheetimmediately after application of the load and a thickness T₁₀ of thesheet after a lapse of 10 hours. The T₁₀/T₀ ratio was taken as anindication of heat resistance.

As the T₁₀/T₀ ratio comes close to 1.0, the heat resistance becomesbetter.

(12) Tensile Test

The tensile strength at break in the direction of extrusion of a sheetwas measured in accordance with JIS K-6767.

Preparation Example 1

Preparation of Ethylene/α-olefin Copolymer (A-1)

Preparation of Catalyst

In 154 liters of toluene, 10 kg of silica having been dried at 250° C.for 10 hours was suspended, and the suspension was cooled to 0° C.Thereafter, 57.5 liters of a toluene solution of methylaluminoxane(Al=1.33 mol/l) was dropwise added over a period of 1 hour. During theaddition, the temperature of the system was maintained at 0° C. Thereaction was successively conducted at 0° C. for 30 minutes. Then, thetemperature of the system was raised up to 95° C. over a period of 1.5hours, and at that temperature, the reaction was conducted for 20 hours.Thereafter, the temperature of the system was lowered to 60° C., and thesupernatant liquid was removed by decantation. The resulting solidcomponent was washed twice with toluene and then resuspended in 100liters of toluene. To the system, 16.8 liters of a toluene solution ofbis(1,3-dimethylcyclopentadienyl)zirconium dichloride (Zr=27.0 mmol/1)was dropwise added at 80° C. over a period of 30 minutes, and thereaction was further conducted at 80° C. for 2 hours. Then, thesupernatant liquid was removed, and the remainder was washed twice withhexane to obtain a solid catalyst containing zirconium in an amount of3.5 mg per gram of the solid catalyst.

Preparation of Prepolymerized Catalyst

To 87 liters of hexane containing 2.5 mol of triisobutylaluminum, 870 gof the above-obtained solid catalyst and 260 g of 1-hexene were added,and prepolymerization of ethylene was conducted at 35° C. for 5 hours toobtain a prepolymerized catalyst wherein an ethylene polymer had beenproduced by prepolymerization in an amount of 10 g per gram of the solidcatalyst.

Polymerization

In a continuous type fluidized bed gas phase polymerization apparatus,copolymerization of ethylene and 1-hexene was conducted at apolymerization temperature of 80° C. under a total pressure of 20kg/cm²-G. To the system were continuously fed the above-obtainedprepolymerized catalyst at a rate of 0.33 mmol/hr in terms of azirconium atom and triisobutylaluminum at a rate of 10 mmol/hr. Duringthe polymerization, ethylene, 1-hexene, hydrogen and nitrogen werecontinuously fed to maintain the gas composition constant (gascomposition: 1-hexene/ethylene=0.038, hydrogen/ethylene=16×10⁻⁴,ethylene concentration=70%)

The yield of the resulting ethylene/α-olefin copolymer (A-1) was 60kg/hr, the density of the copolymer was 0.915 g/cm³, MFR thereof was 3.5g/10 min, and the amount of the decane-soluble component at roomtemperature was 0.48% by weight. The properties of the ethylene/α-olefincopolymer (A-1) are set forth in Table 1.

Example 1

To 100 parts by weight of the ethylene/α-olefin copolymer (A-1), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF, cell uniformity and heat resistance. The results areset forth in Table 2.

Preparation Example 2

Preparation of Ethylene/o-olefin Copolymer Composition (B-1)

An ethylene/α-olefin copolymer (a-4) (density: 0.915 g/cm³) and anethylene/α-olefin copolymer (b-4) (density: 0.933 g/cm³) were eachprepared in the same manner as in Preparation Example 1, except that atitanium catalyst component described in Japanese Patent Publication No.54289/1988 was used instead ofbis(1,3-dimethylcyclopentadienyl)zirconium dichloride, triethylaluminumwas used instead of methylaluminoxane, and the gas composition ratio waschanged as shown in Table 1. The ethylene/α-olefin copolymers (a-4) and(b-4) were melt kneaded in a weight ratio of 60/40 ((a-4)/(b-4)) toobtain an ethylene/α-olefin copolymer composition (B-1). The propertiesof the ethylene/α-olefin copolymer composition (B-1) are set forth inTable 1.

Comparative Example 1

To 100 parts by weight of the ethylene/α-olefin copolymer composition(B-1), 20 parts by weight of butane and 1 part by weight of talc wereadded, and they were melt kneaded and then extrusion foamed by anextruder to prepare a foamed sheet having a thickness of 1 mm. Thefoamed sheet was evaluated on TREE, cell uniformity and tensilestrength. The results are set forth in Table 2.

Comparative Example 2

To 100 parts by weight of a polymer (B-2) (EXACT 3029, available fromExxon Chemical Co., MFR: 3.9 g/10 min, density: 0.915 g/cm³), 20 partsby weight of butane and 1 part by weight of talc were added, and theywere melt kneaded and then extrusion foamed by an extruder to prepare afoamed sheet having a thickness of 1 mm. The foamed sheet was evaluatedon TREF, cell uniformity and heat resistance. The results are set forthin Table 2.

Preparation Example 3

Preparation of Ethylene/α-olefin Copolymer (A-2)

An ethylene/α-olefin copolymer (A-2) was prepared in the same manner asin Preparation Example 1, except that the reaction conditions werecontrolled so as to obtain a copolymer having MFR and a density shown inTable 1.

Example 3

To 100 parts by weight of the ethylene/α-olefin copolymer (A-2), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Preparation Example 4

Preparation of Ethylene/α-olefin Copolymer (A-3)

An ethylene/α-olefin copolymer (A-3) was obtained in the same manner asin Preparation Example 1, except that the reaction conditions werecontrolled so as to obtain a copolymer having MFR and a density shown inTable 1.

Example 2

To 100 parts by weight of the ethylene/α-olefin copolymer (A-3), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Preparation Example 5

Preparation of Ethylene/α-olefin Copolymer (A-4)

Preparation of Catalyst

A polymerization catalyst was obtained in the same manner as in thepreparation of catalyst component in Preparation Example 1, except that2.9 liters of a toluene solution ofbis(1,3-dimethylcyclopentadienyl)zirconium dichloride (Zr: 28.1 mmol/l)and 10.9 liters of a toluene solution ofbis(1,3-n-butylmethylcyclopentadienyl)zirconium dichloride (Zr: 34.0mmol/l) were used instead of 16.8 liters of the toluene solution ofbis(1,3-dimethylcyclopentadienyl)zirconium dichloride.

Polymerization

An ethylene/α-olefin copolymer (A-4) was obtained in the same manner asin Preparation Example 1, except that the above-obtained polymerizationcatalyst was used so as to obtain a copolymer having a density and MFRshown in Table 1.

The properties of the ethylene/α-olefin copolymer (A-4) are set forth inTable 1.

Example 4

To 100 parts by weight of the ethylene/α-olefin copolymer (A-4), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Preparation Example 6

Preparation of Ethylene/α-olefin copolymer (A-5)

Preparation of Catalyst

A polymerization catalyst was obtained in the same manner as in thepreparation of catalyst component in Preparation Example 1, except thatethylenebis(indenyl)zirconium dichloride was used instead ofbis(1,3-dimethylcyclopentadienyl)zirconium dichloride.

Polymerization

An ethylene/α-olefin copolymer (A-5) was obtained in the same manner asin Preparation Example 1, except that the above-obtained polymerizationcatalyst was used so as to obtain a copolymer having a density and MFRshown in Table 1. The properties of the ethylene/α-olefin copolymer(A-5) are set forth in Table 1.

Example 5

To 100 parts by weight of the ethylene/α-olefin copolymer (A-5), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Example 6

To 100 parts by weight of the ethylene/α-olefin copolymer (A-1), 10parts by weight of azodicarbonamide (decomposition type blowing agent)was added, and they were melt kneaded and then extruded by an extruderto obtain a sheet. The sheet was irradiated with electron rays of 4 Mradto prepare a crosslinked sheet. The crosslinked sheet was heated to 230°C. to prepare a foamed sheet. The foamed sheet was evaluated on TREF andcell uniformity. The results are set forth in Table 2.

Preparation Example 7

Preparation of Ethylene/α-olefin Copolymer (A-6)

Preparation of Catalyst

A polymerization catalyst was obtained in the same manner as in thepreparation of catalyst component in Preparation Example 1, except thatbis)1-methyl-3-n-butylcyclopentadienyl)zirconium dichloride was usedinstead of bis(1,3-dimethylcyclopentadienyl)zirconium dichloride.

Polymerization

An ethylene/α-olefin copolymer (A-6) was obtained in the same manner asin Preparation Example 1, except that the above-obtained polymerizationcatalyst was used so as to obtain a copolymer having a density and MFRshown in Table 1 and the gas composition was changed so as to give a1-hexene/ethylene ratio of 0.02, a hydrogen/ethylene ratio of 4.6×10⁻⁴and an ethylene concentration of 70%. The properties of theethylene/α-olefin copolymer (A-6) are set forth in Table 1.

Example 7

To 100 parts by weight of the ethylene/α-olefin copolymer (A-6), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF, cell uniformity, heat resistance and tensilestrength. The results are set forth in Table 2.

Preparation Example 8

Preparation of Ethylene/α-olefin Copolymer (A-7)

An ethylene/α-olefin copolymer (A-7) was obtained in the same manner asin Preparation Example 4, except that the reaction conditions werecontrolled so as to obtain a copolymer having MFR and a density shown inTable 3. The properties of the ethylene/α-olefin copolymer (A-7) are setforth in Table 1.

Example 8

To 100 parts by weight of the ethylene/α-olefin copolymer (A-7), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Preparation Example 9

Preparation of Ethylene/α-olefin Copolymer (A-8)

An ethylene/α-olefin copolymer (A-8) was obtained in the same manner asin Preparation Example 4, except that the reaction conditions werecontrolled so as to obtain a copolymer having MER and a density shown inTable 3. The properties of the ethylene/α-olefin copolymer (A-8) are setforth in Table 1.

TABLE 1 Comonomer MFR n-decane Co- Content g/10 Density soluble TM MT FIpolymer Type mol % min Mw/Mn g/cm³ part wt % *1 ° C. *2 g *3 S⁻¹ *4 A-11- 4.0 3.5 2.8 0.915 0.48 2.52 114.2 116.0 1.0 0.77 570 260 hexene A-21- 2.5 1.5 2.9 0.923 0.41 1.19 115.8 119.2 2.3 1.56 280 110 hexene A-31- 5.1 1.4 2.8 0.905 2.05 6.67 110.7 112.0 2.6 1.66 270 110 hexene B-11- 4.8 4.2 4.8 0.918 8.9  1.89 122.6 117.2 0.44 0.66 510 320 hexene B-21- 3.5 3.9 2.0 0.915 0.31 2.52 107.7 116.0 0.44 0.70 220 290 hexene A-41- 2.5 1.7 2.6 0.922 0.43 1.30 116.0 118.8 2.3 1.41 200 130 hexene A-51- 3.0 1.5 4.4 0.920 0.44 1.57 114.8 118.0 5.0 1.56 520 110 hexene A-61- 4.1 4.0 2.1 0.915 0.50 2.52 113.9 116.0 250 300 hexene A-7 1- 3.0 4.00.921 0.25 1.43 115.0 118.4 250 300 hexene A-8 1- 5.3 4.3 0.904 2.107.36 110.2 111.6 260 320 hexene *1 Value of 80 × exp (−100(d − 0.88) +0.1 *2 Value of 400 × d − 250 *3 Value of 2.2 × MFR^(−0.84) *4 Value of75 × MFR

Example 9

To 100 parts by weight of the ethylene/α-olefin copolymer (A-8), 20parts by weight of butane and 1 part by weight of talc were added, andthey were melt kneaded and then extrusion foamed by an extruder toprepare a foamed sheet having a thickness of 1 mm. The foamed sheet wasevaluated on TREF and cell uniformity. The results are set forth inTable 2.

Example 10

To 100 parts by weight of the ethylene/α-olefin copolymer (A-6), 10parts by weight of azodicarbonamide (decomposition type blowing agent)was added, and they were melt kneaded and then extruded by an extruderto obtain a sheet. The sheet was irradiated with electron rays of 4 Mradto prepare a crosslinked sheet. The crosslinked sheet was heated to 230°C. to prepare a foamed sheet. The foamed sheet was evaluated on TREF andcell uniformity. The results are set forth in Table 2.

Example 11

A foamed sheet was prepared in the same manner as in Example 10, exceptthat the copolymer (A-7) was used instead of the ethylene/α-olefincopolymer (A-6) The foamed sheet was evaluated on TREF and celluniformity. The results are set forth in Table 2.

Example 12

A foamed sheet was prepared in the same manner as in Example 10, exceptthat the copolymer (A-8) was used instead of the ethylene/α-olefincopolymer (A-6). The foamed sheet was evaluated on TREF and celluniformity. The results are set forth in Table 2.

TABLE 2 Cell TREF Expans- uni- Tensile Co- % ion formity strengthExample polymer *5 ratio *6 t₁₀/t₀ (MPa) Ex. 1 A-1 3.3 30 ∘ 0.93 Comp.B-1 40.1 13 x  5 Ex. 1 Comp. B-2 0.0 25 ∘ 0.65 Ex. 2 Ex. 2 A-2 4.9 34 ∘Ex. 3 A-3 1.5 35 ∘ Ex. 4 A-4 4.8 34 ∘ Ex. 5 A-5 4.5 38 ∘ Ex. 6 A-1 3.335 ∘ Ex. 7 A-6 3.5 25 ∘ 0.92 20 Ex. 8 A-7 4.8 25 ∘ Ex. 9 A-8 1.3 26 ∘Ex. 10 A-6 3.5 30 ∘ Ex. 11 A-7 4.8 30 ∘ Ex. 12 A-8 1.3 30 ∘ *5 Elutionamount at 100° C. or above in the TREF elution curve *6 ∘: excellentuniformity x: poor uniformity

What is claimed is:
 1. An ethylene resin foamed product comprising anethylene/α-olefin copolymer which is a copolymer of ethylene and anα-olefin of 3 to 12 carbon atoms and meets the following requirements:(i) the density is in the range of 0.880 to 0.940 g/cm³, (ii) the meltflow rate (MFR) at 190° C. under a load of 2.16 kg is in the range of0.1 to 20 g/10 min, (iii) the decane-soluble component fraction (W (% byweight)) at room temperature and the density (d (g/cm³)) satisfy thefollowing relation in case of MFR≦10 g/10 min:W<80×exp(−100(d−0.88))+0.1, in case of MFR>10 g/10 min:W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1,  and (iv) the temperature (Tm(° C.)) at the maximum peak position in the endothermic curve asmeasured by a differential scanning calorimeter (DSC) and the density (d(g/cm³)) satisfy the following relation Tm<400×d−250.
 2. The ethyleneresin foamed product as claimed in claim 1, wherein theethylene/α-olefin copolymer further meets, in addition to therequirements (i) to (iv), the following requirements: (v) the flow index(FI (1/sec)), which is defined as a shear rate at which the shear stressof said copolymer in a molten state at 190° C. reaches 2.4×10⁶ dyne/cm²,and the melt flow rate (MFR (g/10 min)) satisfy the following relationFI>75×MFR,  and (vi) the melt tension (MT (g)) at 190° C. and the meltflow rate (MFR (g/10 min)) satisfy the following relation MT>2.2×MFR^(−0.84).
 3. The ethylene resin foamed product as claimed in claim 1,wherein the ethylene/α-olefin copolymer further meets, in addition tothe requirements (i) to (iv), the following requirements: (vii) the flowindex (FI (1/sec)), which is defined as a shear rate at which the shearstress of said copolymer in a molten state at 190° C. reaches 2.4×10⁶dyne/cm², and the melt flow rate (MFR (g/10 min)) satisfy the followingrelation FI>150×MFR,  and (viii) the melt tension (MT (g)) at 190° C.and the melt flow rate (MFR (g/10 min)) satisfy the following relationMT>4.0×MFR^(−0.65).
 4. The ethylene resin foamed product as claimed inclaim 1, wherein the ethylene/α-olefin copolymer is a copolymer of 4 to12 carbon atoms and further meets, in addition to the requirements (i)to (iv), the following requirements: (ix) the flow index (FI (1/sec)),which is defined as a shear rate at which the shear stress of saidcopolymer in a molten state at 190° C. reaches 2.4×10⁶ dyne/cm², and themelt flow rate (MFR (g/10 min)) satisfy the following relationFI≦75×MFR.
 5. The ethylene resin foamed product as claimed in any one ofclaims 1 to 4, wherein the ethylene/α-olefin copolymer is a copolymerobtained by copolymerizing ethylene and an α-olefin of 3 to 12 carbonatoms in the presence of an olefin polymerization catalyst comprising:(a) a compound of a transition metal of Group IV of the periodic table,which contains a ligand having cyclopentadienyl skeleton, and (b) anorganoaluminum oxy-compound.
 6. The ethylene resin foamed product asclaimed in any one of claims 1 to 4, wherein when the ethylene/α-olefincopolymer is subjected to a temperature rise elution test (TREF), acomponent that is eluted at a temperature of not lower than 100° C. ispresent in the copolymer and the amount of the component that is elutedat a temperature of not lower than 100° C. is not more than 10% of thewhole elution amount.
 7. An ethylene resin foamed product comprisingcrosslinked polyethylene obtained by crosslinking the ethylene/α-olefincopolymer of any one of claims 1 to
 4. 8. The ethylene resin foamedproduct as claimed in claim 5, wherein when the ethylene/α-olefincopolymer is subjected to a temperature rise elution test (TREF), acomponent that is eluted at a temperature of not lower than 100° C. ispresent in the copolymer and the amount of the component that is elutedat a temperature of not lower than 100° C. is not more than 10% of thewhole elution amount.
 9. An ethylene resin foamed product comprisingcrosslinked polyethylene obtained by crosslinking the ethylene/α-olefincopolymer of claim
 5. 10. An ethylene resin foamed product comprisingcrosslinked polyethylene obtained by crosslinking the ethylene/α-olefincopolymer of claim
 6. 11. An ethylene resin foamed product comprisingcrosslinked polyethylene obtained by crosslinking the ethylene/α-olefincopolymer of claim 8.